This invention relates to magnetic tape drives and more particularly, to a system for monitoring the vacuum and pressure which control the movement of magnetic tape in the drive.
High speed, high density magnetic tape drives are extensively used for storing digital data in computer systems. The tape drive supplied by Storage Technology Corporation under its model designation 1950 is a typical drive which uses vacuum and pressure to control the movement of magnetic tape in the drive. The pneumatic system for this tape drive is shown in U.S. Pat. No. 4,331,306--Epina, et al, issued May 25, 1982. In this tape drive ten discrete pressure and vacuum switches provide pneumatic sense information which indicates the completion or presence of normal drive conditions or they indicate that pneumatic levels have fallen below operational values due to pneumatic system component failure, such as broken drive belts, stuck air valves, loose hoses and the like. The cost of these multiple pressure and vacuum switches is significant. More importantly, these separate pressure and vacuum sensors sometimes detract from the reliability of the system. The sensors themselves are subject to failure and their failure causes the tape drive to be taken out of operation while the fault is diagnosed. While it is important that pressure and vacuum be maintained at the ten discrete locations at which they are presently sensed, a variation in the vacuum or pressure from normal at any given location is not necessarily critical to the operation. In the prior art, these sense switches are connected in an operate/not operate mode. When any one sensor indicates that the pressure or vacuum at its location is out of limits, the operation of the machine stops while the problem is diagnosed. The more desirable mode of operation is to determine whether the overall pneumatic system is above or below the capability for which normal operation is obtained. If a variation in the pneumatic system occurs, but it does not bring the entire system below that capability, then it is desirable to permit continued operation of the machine, but to provide an indication of the deviation so that it can be checked during routine maintenance.
Furthermore, the prior art sensors are subject to changes in ambient pressure. Significant changes in ambient pressure, such as occurs at different altitudes, require that drive pneumatic levels be re-adjusted to accommodate this change.
It is an object of the present invention to provide a pneumatic monitoring system which more reliably indicates the capability of the tape drive.
It is another object of the present invention, to provide a pneumatic monitoring system for a magnetic tape drive which automatically compensates for changes in ambient pressure.
It is another object of the present invention, to provide a monitoring system for a magnetic tape drive which accurately locates the failure in the pneumatic system.
It is another object of the present invention to provide a monitoring system for a magnetic tape drive which allows continued operation despite slightly marginal pneumatic conditions (due to small leaks, etc.) while flagging the soft failure for correction during normal maintenance.